Corrosion resistant grease compositions



United States Patent O 3,227,651 CORROSION RESISTANT GREASE COMPOSITIONSBertil A. Peterson, Amityville, N.Y., assignor to Socony Mobil OilCompany, Inc., a corporation of New York N Drawing. Filed Sept. 27,1963, Ser. N 0. 311,973 Claims. (Cl. 25221) This application is acontinuation-in-part of my copending application Serial No. 227,531,filed October 1, 1962.

This invention relates to lubricating grease compositions suitable foruse over a wide range of operating conditions. In one of its aspects,the invention relates to lubricating grease compositions containingcertain ma terials which exhibit corrosion or rust-inhibiting characteristics when incorporated in these greases. Still more particularly,in this aspect, the invention relates to lubricating grease compositionsexhibiting the aforementioned corrosion inhibiting characteristics andto a method for their preparation.

Grease compositions, in general, comprise a lubricating vehicle,thickened to a grease consistency with gelling or grease-forming agents,which may comprise metallic salts and soaps of organic acids of varyingmolecular weights present in various compositions thereof. These greasecompositions, depending upon the environment in which they are employed,may be continuously or inter mittently subjected to humid or wetatmospheric conditions, where moisture, even when present in relativelyminor amounts, results in the corrosion of the metallic surface beinglubricated. In an attempt to minimize or to avoid these corrosionphenomena, various means have been investigated which include theincorporation of corrosion or rust inhibiting materials into the greasecornpositions themselves.

Among the corrosion inhibiting materials that have been suggested forincorporation into grease compositions, are the water soluble nitritesor chromates, which are well known for their corrosion inhibitingproperties. In particular, they comprise the alkali metal nitrites orchromates, and may also include the amine and ammonium nitrites andchromates. Of particular importance is sodium nitrite, which has beenemployed in various grease compositions in amounts varying from about0:1 to about 1 percent by weight of the total soap. This material isgenerally employed in the form of an aqueous solution, although it hasalso been utilized in substantially anhydrous greases, as well. It hasbeen found, however, that in order to make this material commerciallyfeasible for use as a corrosion inhibitor in greases, it is necessarythat the size of the dispersed sodium nitrite crystals be maintainedbelow approximately 5 microns, in order to minimize abrasion of themetallic surfaces being lubricated by the grease. In this respect, ithas been found that in practicing the method of the prior art in whichsodium nitrite solutions are added to the grease during processing, andfollowed by the removal of Water by dehydration, there results theformation of sodium nitrite crystals which are considerably larger insize than 5 microns. To overcome this undesirable tendency of largesodium nitrite crystal-formation, various methods have been resorted to,which have included high temperature spraydrying of sodium nitrite oiland water emulsions, or ball milling of dry sodium nitrite dispersed inoil or in grease, in order to maintain the sodium nitrite crystals at asmall size. These methods have not, however, proven to be completelysatisfactory. Thus, prior to the present invention, no effective andrelatively simple method has been proposed for the incorporation ofsodium nitrite, as a corrosion inhibiting agent, into greasecompositions,

in which these crystals are present in relatively small sizes.

It is, therefore, an object of the present invention to provide animproved grease composition.

Another object of the invention is to provide grease compositions havingimproved corrosion-inhibiting properties, and wherein metallic surfacesbeing lubricated with grease containing them are not significantlyabraded.

A still further object of the invention is to provide improved greasecompositions having the aforementioned characteristics, and a method fortheir preparation.

Other objects and advantages inherent in the invention will becomeapparent to those skilled in the art from the following disclosure.

It has now been found that greases containing the improvedcorrosion-inhi'biting compositions hereinafter discussed have overcomethe disadvantages heretofore encountered in commercial applications,resulting in obtaining a grease of improved corrosion-inhibitingproperties, and in which the corrosion-inhibiting agent itself does notimpose any significant degree of abrasion upon the surfaces beinglubricated. In general, the improved corrosion-inhibitor of the presentinvention comprises an alkali metal nitrite, a lubricating vehicle, anda thickening or gelling agent, and which, when prepared in accordancewith the improved method of the invention, results in obtainingcorrosion-inhibiting compositions in which the alkali metal nitritecrystals are present in a relatively small average size (i.e., belowapproximately 5 microns), so that the desirable corrosion inhibitingproperties are attained by reason of their presence, and yet are toosmall in size to cause any significant degree of abrasion upon themetallic surfaces which are lubricated with greases containing them.

Insofar as the components comprising the corrosioninhi-bitor areconcerned, the alkali metal nitrites that may be employed include sodiumnitrite, potassium nitrite and lithium nitrite. Of these sodium nitriteis preferred. The alkali metal nitrite is employed in the inhibitorcomposition in an amount from about 5 to about 60 percent by weight,preferably in an amount from about 10 to about 50 percent by weight, andcomprises from about 0.05 percent to about 2 percent by weight, of thetotal grease composition.

The lubricating vehicle employed in the inhibitor composition maycomprise any of the conventional hydrocarbon oils of lubricatingviscosity and may include mineral or synthetic lubricating oils,aliphatic phosphates, esters and diesters, silicates, siloxanes andoxalkyl ethers and esters. Mineral lubricating oils, which are preferredas the lubricating vehicle, may be of any suitable lubricating viscosityranging from about 45 SSU at 100 F., to about 2000 SSU at 100 F. andpreferably from about 50 to about 250 SSU at 210 F. These oils may haveviscosity indexes, varying from below 0 to about 100 or higher.Viscosity indexes from about 70 to about are preferred. The averagemolecular weights of these oils range from about 250 to about 800. Thislubricating vehicle is employed in the inhibitor in an amount suflicientto constitute the balance of the inhibitor composition, after accountingfor the desired specific quantities of alkali metal nitrate, andthickening agents, in a given instance.

The thickening or gelling agent employed in the inhibitor compositioncomprises an essentially hydrophobic clay. This thickening agent may beprepared from a clay which is initially hydrophilic in character, butwhich has been converted into a hydrophobic condition by theintroduction of long chain hydrocarbon radicals into the surface of theclay particles, prior to its use as a component of the inhibitorcomposition, as, for example, by being subjected to a preliminarytreatment with organic cationic surface active agents, such as oniumcompounds. This method of conversion, being well known to those skilledin the art, is believed to require no further discussion, and does notform a part of the present invention.

More specifically, the clays which are useful as starting materials informing the thickening agents to be employed in the inhibitorcomposition, may comprise the naturally occurring chemically unmodifiedclays. These clays are crystalline complex silicates, the exactcomposition of which is not subject to precise description, since theyvary widely from one natural source to another. These clays may bedescribed as complex inorganic silicates such as aluminum silicates,magnesium silicates, barium silicates, and the like, containing, inaddition to the silicate lattice, varying amounts of cation-exchangeablegroups generally regarded as metallic oxide radicals. Hydrophilic clayswhich are particularly useful for conversion to the thickening agents ofthe present corrosion-inhibitor include montmorillonite clays, e.g.bentonite, attapulgite, hectorite, illite, saponite, sepiolite, biotite,vermiculite, zeolite clays, and the like. The thickening agent isemployed in the inhibitor composition in an amount from about 0.5percent to about 30 percent by weight, and preferably from about 3percent to about percent by weight, and comprises from about .02 percentto about 2.0 percent of the total grease composition, by weight.

The preparation of the improved inhibitor composition, in accordancewith the process of the present invention, comprises, in general,preparing a mixture in the form of a dispersion of the lubricatingvehicle and the thickening agent; preparing an aqueous mixture of thealkali metal nitrite and water; combining the two mixtures, forming anemulsion; and then susbtantially dehydrating the resulting combinedmixture to produce the desired inhibitor composition, in which form itis ready for incorporation into specific lubricating greasecompositions.

In preparing the mixture or dispersion of the lubricating vehicle andthe thickening agent, an open grease kettle is preferably employed, intowhich the required quantities of lubricating vehicle and thickeningagent are charged. The aqueous mixture of the alkali metal nitrite andwater, which is also charged to the open grease kettle, is prepared byfirst dissolving the alkali metal nitrite in water, in such quantitiesas to obtain a mixture of desired concentration of these components. Thecombined mixture thus formed is heated to a temperature below about 212F., and preferably to a temperature between about 175 F. and about 205F. to insure a uniform dispersion of water and oil components. The abovementioned combined mixtures are then homogenized at elevated pressure,and the kettle is maintained at a temperature not higher than about 212F. for a suflicient time to permit thorough admixture of the components.Thereafter, in order to effect dehydration of the combined material, thekettle temperature is gradually increased to a temperature from about290 F., to about 300 F.

The following examples will serve to illustrate the preparation oftypical improved corrosion-inhibitor compositions of the presentinvention, and their incorporation and performance in greasecompositions.

Example 1 Percent by Pounds Weight Bpntnna 4. 39 1. S0 Mineral Oil, 75"at 100 F 73. 41 30. 14 Sodium nitrite 22. 9. 13

In preparing the above dispersion, an open kettle was charged with 30.14pounds of the mineral oil. To the oil were then added 1.8 pounds ofcommercial Bentone, While recycling through a Manton-Gaulin homogenizerat a pressure of about 3000 p.s.i. 9.13 pounds of sodium nitrite werenext separately dissolved in 8 pounds of water. Solution of the sodiumnitrite was eifected by heating this mixture to a temperature of 180 F.This aqueous solution of sodium nitrite was then added to the Bentonedispersion in the mineral oil in the kettle, and the combined mixture inthe kettle was homogenized, employing a Manton-Gaulin homogenizer, at apressure of about 3000 to about 3500 p.s.i. The kettle was heated andthe temperature was controlled at approximately 205 F. for a period of30 minutes, while homogenizing was taking place. After this time, thekettle temperature was gradually increased to a temperature ofapproximately 290 F., at which point the material was found to besubstantially dry. Examination of the crystal size of the dispersedsodium nitrite particles in the thus prepared composition, showed anaverage particle size of less than 3 microns.

Example 2 Percent by Pounds Weight Bentone-thickcncd grease 38. 15. 97Mineral oil, 75" at 100 F 38. 90 15. 97 Sodium nitrite 2'2. 20 9. 13

In preparing the above dispersion, an open kettle was charged with 15.97pounds of the Bentone-thickening grease, and 15.97 of the mineral oil.This mixture was recycled through a Manton-Gaulin homogenizer, operatingat a pressure of about 3000 to about 3500 p.s.i. until a homogeneous gelhad formed. This gel was heated to a temperature of about F. and at thistemperature 9.13 pounds of sodium nitrite dissolved in 8 pounds of waterwas added. This mixture was next dehydrated while homogenizing byheating to a temperature of approximately 300 F. After dehydration hadtaken place, examination of the crystal size of the dispersed sodiumnitrite particles in the thus prepared composition, showed an averageparticle size of less than one micron.

Grease compositions, containing the above described corrosion inhibitorsof the present invention, when subjected to a hearing test, conducted inaccordance with the specifications of ASTM D1743-60T or by the CRCL-41test, reveal a rating of No. 1, indicating the absence of any corrosiveeffect upon the bearing surfaces being treated. Thus, as indicatedabove, the improved corrosion-inhibitor compositions of the presentinvention may be incorporated in many grease compositions and have awide variety of industrial applications.

As previously indicated it is necessary that the thickening agent of thenovel inhibitor composition comprises an essentially hydrophobic clayand that this clay can be prepared from a clay which is initiallyhydrophilic in character. The use of hydrophilic clays, on the otherhand, does not result in obtaining the improved inhibitor compositionsof the present invention in which the nitrite particle size is below 5microns. To illustrate this criticality, an attempt was made to employcommercially available bentonite, a hydrophilic clay, as the thickeningagent, as shown in the following example.

Example 3 Percent by Grams Weight Bentonite 4. 39 43. 9 Mineral oil, 75at 100 73. 41 734. 1 Sodium nitrite 22. 20 222.

In preparing the above composition, a dispersion was attempted to bemade by mixing 43.9 grams of bentonite with approximately 734.1 grams ofthe mineral oil, by passing the mixture through a homogenizer, in sixtries. No gel was obtained. To 387.3 grams of this mixture a solutioncomprising approximately 111 grams of sodium nitrite in 100 grams ofwater was added. This mixture was stirred and then passed through thehomogenizer for another six times. After homogenization had taken place,it was found that the bentonite had absorbed the aqueous solution ofsodium nitrite, forming a paste or a gel. The mineral oil, however, hadseparated out to form a distinct layer.

It will also be understood that by following the procedure such asillustrated by the above Examples 1, 2 and 3 other alkali metal nitritesmay be substituted for the sodium nitrite employed in the presentcorrosion-inhibitor composition. Similarly, other lubricating vehicles,dispersing and thickening agents, as disclosed above, may be alsosubstituted in these compositions, in various combinations, if sodesired. It will also be understood that any of the corrosion-inhibitorcompositions prepared in accordance with the process of the presentinvention, may be incorporated in a wide variety of grease compositions,in addition to those described in the examples.

While preferred embodiments of the compositions of the present inventionand the process for their preparation have been described for thepurpose of illustration, it should be understood that variousmodifications and adaptations thereof, which will be obvious to thoseskilled in the art, may be made without departing from the spirit of theinvention.

I claim:

1. A metal soap-thickened grease composition containing a corrosioninhibitor, said inhibitor comprising from about 5 to about 60 percent,by weight, of an alkali metal nitrite having an average particle sizebelow about 5 microns; from about 0.5 to about 30 percent, by Weight, ofa thickening agent comprising an essentially hydrophobic clay; and anoil of lubricating viscosity as a vehicle.

2. A metal soap-thickened grease composition containing a corrosioninhibitor, said inhibitor comprising from about 10 to about percent, byweight, of an alkali metal nitrite having an average particle size belowabout 5 microns; from about 3 to about 15 percent, by weight, of athickening agent comprising an essentially hydrophobic clay, and an oilof lubricating viscosity as a vehicle.

3. A metal soap-thickened grease composition containing a corrosioninhibitor, said inhibitor comprising from about 5 to about percent, byweight, of an alkali metal nitrite having an average particle size belowabout 5 microns; from about 0.5 to about 30 percent, by weight, of athickening agent comprising an amine-exchanged montmorillonite clay, andan oil of lubricating viscosity as a vehicle.

4. A metal soap-thickened grease composition containing a corrosioninhibitor, said inhibitor comprising from about 10 to about 50 percent,by Weight, of sodium nitrite having an average particle size below about5 microns; from about 3 to about 15 percent, by weight, of a thickeningagent comprising an amine-exchanged montmorillonite clay; and an oil oflubricating viscosity as a vehicle.

5. A metal soap-thickened grease composition containing a corrosioninhibitor, said inhibitor comprising, by weight, a major proportion ofan alkali metal nitrite having an average particle size below about 5microns; a minor proportion of a thickening agent comprising anessentially hydrophobic clay, and an oil of lubricating viscosity as avehicle.

References Cited by the Examiner UNITED STATES PATENTS 3,065,176 11/1962Blake et al 252--25 3,089,848 5/ 1963 Morway 25225 FOREIGN PATENTS875,732 8/ 1961 Great Britain.

OTHER REFERENCES Higher Diols, by Carbide and Carbon Chemicals Corp.,received in Patent Office March 27, 1950, 8 pages. The CondensedChemical Dictionary, Sixth ed., 1961, Reinhold Pub. Corp., New York,pages 540 and 735.

DANIEL E. WYMAN, Primary Examiner.

j UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,227,651 January 4, 1966 Bertil A. Peterson It is hereby certified.that error appears in the above numbered patent requiring correction andthat the said Letters Patent should read as corrected below.

Column 2, line 61, for "nitrate" read nitrite column 3, line 31, for"susbtantially" read substantially Signed and sealed this 13th day ofDecember 1966.

- (SEAL Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Commissioner of Patents AttestingOfficer UNITED STATES "PATENT OFFICE CERTIFICATE OF CORRECTION PatentNo. 3,227,651 January 4, 1966 Bertil A. Peterson ears in the abovenumbered pat- It is hereby certified that error app Letters Patentshould read as ent requiring correction and that the said correctedbelow.

Column 2, line 61, for "nitrate" read nitrite column 3, line 31, for"susbtantially" read substantially Signed and sealed this 13th day ofDecember 1966.

(SEAL Attest: ERNEST W. SWIDER EDWARD J. BRENNER Amting OfficerCommissioner of Patents

1. A METAL SOAP-THICKENED GREASE COMPOSITION CONTAINING A CORROSIONINHIBITOR, SAID INHIBITOR COMPRISING FROM ABOUT 5 TO ABOUT 60 PERCENT,BY WEIGHT, OF AN ALKALI METAL NITRITE HAVING AN AVERAGE PARTICLE SIZEBELOW ABOUT 5 MICRONS; FROM ABOUT 0.5 TO ABOUT 30 PERCENT, BY WEIGHT, OFA THICKENING AGENT COMPRISING AN ESSENTIALLY HYDROPHOBIC CLAY; AND ANOIL OF LUBRICATING VISCOSITY AS A VEHICLE.